Head for harvesting of trees and vehicle provided with the improved head

Abstract

The invention relates to an improved head for harvesting of trees. In particular, the head according to the invention is an improvement of a head for harvesting of trees as disclosed in European Patent EP2515628, which state of art is hereby incorporated by reference. In the known head, the balance between the saw pressure and the saw speed is controlled by the oil pressure at the inlet port of the hydraulic motor. This has the drawback that the saw pressure is depending on the saw speed. It is the aim of the invention to provide an improved head for harvesting trees, wherein the saw pressure is constant and independent of the saw speed.

The invention claimed is: 
     
       1. A hydraulically controlled head ( 2 ) for harvesting trees, which head is arranged for attachment on a vehicle ( 1 ) with a hydraulic pump unit, which head ( 2 ) comprises a
 double-action hydraulic valve ( 6 ) for connecting to the hydraulic pump unit, 
 a clamp ( 7 ) for placement round a tree, comprising a first hydraulic actuator ( 12 ) 
 a tilting device ( 9 ) for tilting the clamp ( 7 ), comprising a second hydraulic actuator ( 10 ), 
 a chainsaw ( 13 ) for sawing through a clamped tree, comprising a hydraulic motor ( 14 ), 
 a saw displacement device for causing the blade of the chainsaw to move out of and into a saw casing, comprising a third hydraulic actuator ( 15 ) and 
 a first pressure line ( 5   a ) and a second pressure line ( 5   b ), the first pressure line ( 5   a ) and the second pressure line ( 5   b ) each connecting the hydraulic valve ( 6 ) to the first hydraulic actuator ( 12 ), the second hydraulic actuator ( 10 ) and the third hydraulic actuator ( 15 ), 
 the hydraulic motor ( 14 ) comprises an inlet port ( 21 ), a first outlet port ( 22 ) and a drain port ( 27 ), wherein
 the drain port is connected via a first non-return valve ( 29 ) to the first pressure line ( 5   a ) and is provided with a first hydraulic accumulator ( 28 ), 
 
 
       and 
       the first outlet port ( 22 ) is connected via a throttle control valve ( 23 ) and a second non-return valve ( 24 ) to the first pressure line ( 5   a ), and the first inlet port ( 21 ) is connected to the second pressure line ( 5   b ), wherein the third hydraulic actuator ( 15 ) comprises a double-action hydraulic cylinder which is connected to the first outlet port ( 22 ) of the hydraulic motor ( 14 ) and, via a third non-return valve ( 26 ), to a second hydraulic accumulator ( 25 ), and
 a hydraulic control unit suitable for controlling the first hydraulic actuator ( 12 ), the second hydraulic actuator ( 10 ) and the third hydraulic actuator ( 15 ) and the hydraulic motor ( 14 ), 
 
       wherein the head ( 2 ) comprises control means for controlling the saw pressure and the saw speed by the oil pressure at the first outlet port ( 22 ) of the hydraulic motor ( 14 ). 
     
     
       2. A hydraulically controlled head ( 2 ) according to  claim 1 , wherein a pressure relief valve ( 46 ) is provided connecting the first outlet port ( 22 ) to the first pressure line ( 5   a ) such that the pressure relief valve ( 46 ) is connected parallel to the throttle control valve ( 23 ) and the non-return valve ( 24 ). 
     
     
       3. A hydraulically controlled head ( 2 ) according to  claim 2 , wherein the first hydraulic actuator ( 12 ) comprises a double-action hydraulic cylinder for opening and closing the clamp and a load holding valve ( 45 ) is provided which load holding valve ( 45 ) comprises a second inlet port ( 48 ), a third inlet port ( 49 ) and a second outlet port ( 50 ), wherein the second inlet port ( 48 ) is connected to first pressure line ( 5   a ), the third inlet port ( 49 ) is connected to the second pressure line ( 5   b ) and the second hydraulic actuator ( 10 ) comprises a second double-action hydraulic cylinder which is connected to the first pressure line ( 5   a ) and the second outlet port ( 50 ). 
     
     
       4. A hydraulically controlled head ( 2 ) according to  claim 1 , wherein the third hydraulic actuator ( 15 ) comprises a double-action hydraulic cylinder, which is connected to the first outlet port ( 22 ) of the hydraulic motor ( 14 ) via a fourth non-return valve ( 47 ). 
     
     
       5. Vehicle ( 1 ) provided with a hydraulically controlled head ( 2 ) for harvesting trees, which head is arranged for attachment on a vehicle ( 1 ) with a hydraulic pump unit, which head ( 2 ) comprises a
 double-action hydraulic valve ( 6 ) for connecting to the hydraulic pump unit, 
 a clamp ( 7 ) for placement round a tree, comprising a first hydraulic actuator ( 12 ) 
 a tilting device ( 9 ) for tilting the clamp ( 7 ), comprising a second hydraulic actuator ( 10 ), 
 a chainsaw ( 13 ) for sawing through a clamped tree, comprising a hydraulic motor ( 14 ), 
 a saw displacement device for causing the blade of the chainsaw to move out of and into a saw casing, comprising a third hydraulic actuator ( 15 ) and 
 a first pressure line ( 5   a ) and a second pressure line ( 5   b ) for connecting the hydraulic valve ( 6 ) to the first hydraulic actuator ( 12 ), the second hydraulic actuator ( 10 ) and the third hydraulic actuator ( 15 ), 
 the hydraulic motor ( 14 ) comprises an inlet port ( 21 ), a first outlet port ( 22 ) and a drain port ( 27 ), wherein 
 
       the drain port is connected via a first non-return valve ( 29 ) to the first pressure line ( 5   a ) and is provided with a first hydraulic accumulator ( 28 ), and 
       the first outlet port ( 22 ) is connected via a throttle control valve ( 23 ) and a second non-return valve ( 24 ) to the first pressure line ( 5   a ), and the first inlet port ( 21 ) is connected to the second pressure line ( 5   b ), wherein the third hydraulic actuator ( 15 ) comprises a double-action hydraulic cylinder which is connected to the first outlet port ( 22 ) of the hydraulic motor ( 14 ) and, via a third non-return valve ( 26 ), to a second hydraulic accumulator ( 25 ), and
 a hydraulic control unit suitable for controlling the first hydraulic actuator ( 12 ), the second hydraulic actuator ( 10 ) and the third hydraulic actuator ( 15 ) and the hydraulic motor ( 14 ), 
 
       wherein the head ( 2 ) comprises control means for controlling the saw pressure and the saw speed by the oil pressure at the first outlet port ( 22 ) of the hydraulic motor ( 14 ).